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Temperature-Dependent Branching Ratios of Deuterated Methoxy Radicals (CH2DO•) Reacting With O2

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journal contribution
posted on 21.06.2012, 00:00 by Hongyi Hu, Theodore S. Dibble, Geoffrey S. Tyndall, John J. Orlando
The methoxy radical is an intermediate in the atmospheric oxidation of methane, and the branching ratio (k1a/k1b) (CH2DO• + O2 → CHDO + HO2 (1a) and CH2DO• + O2 → CH2O + DO2 (1b)) strongly influences the HD/H2 ratio in the atmosphere, which is widely used to investigate the global cycling of molecular hydrogen. By using the FT-IR smog chamber technique, we measured the yields of CH2O and CHDO from the reaction at 250–333 K. Kinetic modeling was used to confirm the suppression of secondary chemistry. The resulting branching ratios are well fit by an Arrhenius expression: ln­(k1a/k1b) = (416 ± 152)/T + (0.52 ± 0.53), which agrees with the room-temperature results reported in the only previous study. The present results will be used to test our theoretical understanding of the role of tunneling in the methoxy + O2 reaction, which is the prototype for the entire class of alkoxy + O2 reactions.